Page:On the economy of machinery and manufactures - Babbage - 1846.djvu/280

246 a fund, which, with the strictest economy, shall be just sufficient,first, to repay the expense of its original formation;secondly, to maintain it in good and sufficient repair." They first endeavoured to ascertain, from competent persons, the effect of the atmosphere alone in deteriorating a well-constructed road. The next step was, to determine the proportion in which the road was injured, by the effect of the horses' feet compared with that of the wheels. Mr. Macneill, the superintendent, under Mr. Telford, of the Holyhead roads, was examined, and proposed to estimate the relative injury, from the comparative quantities of iron worn off from the shoes of the horses, and from the tire of the wheels. From the data he possessed, respecting the consumption of iron for the tire of the wheels, and for the shoes of the horses, of one of the Birmingham day-coaches, he estimated the wear and tear of roads, arising from the feet of the horses, to be three times as great as that arising from the wheels. Supposing repairs amounting to a hundred pounds to be required on a road travelled over by a fast coach at the rate of ten miles an hour, and the same amount of injury to occur on another road, used only by waggons, moving at the rate of three miles an hour, Mr. Macneill divides the injuries in the following proportions: